I've had this bonus, but I'm not familiar with the upgrade bonus for the CG package. The new funds for the investment bonus may clearly be placed in any Citi-affiliated account or moved anytime between accounts. If you happen to drop below the required threshold due to investment losses, but not due to withdrawals, you won't need to make up the difference with new deposits.
Since I'm not familiar with the package upgrade offer, I won't speculate any further what that might require.